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January 19, 2012

INTRO: First off, I’m sorry this review has taken so long. I started receiving requests to review the FiiO E10 long before it was even available in the US. Finally it became available for a short time from a few US vendors but then disappeared. After many months it appeared again and I managed to borrow one in December to test. But the holidays, travel, and year-end workload, intervened. Since the first of the year I’ve had many unplanned non-audio distractions. But, finally, here’s the long awaited E10 review! Thanks for everyone’s patience.

FiiO E10: The FiiO E10 is a simple Chinese designed and built USB powered headphone DAC designed to outperform the older, but more expensive and feature laden, FiiO E7. It has a USB port, headphone output, line output, coaxial S/PDIF digital output, gain switch, bass EQ switch and a volume control. The E10’s closest popular competitor might be the NuForce uDAC-2 I reviewed in February of last year. The E10 is impressively small and highly portable. It’s typically priced around $80 in the USA making it much cheaper than the flawed uDAC-2.

COMPARED TO FiiO E7: The E10 is missing several E7 features. They include battery operation, a line input allowing use as a headphone amp (for say an iPod or other portable device), multiple EQ settings, microprocessor control, electronic volume adjustment, a digital display and the E9 docking option.

FUTURE FiiO E17: If you miss some of the E7 features, but want the better audio performance of the E10, you might wait for the future E17. But, if it’s anything like the E10’s USA introduction, be prepared to wait a while. FiiO seems to be having problems with manufacturing, distribution, and/or releasing products too early.

E10 VERSIONS: Some speculated FiiO revised the E10 during the several months it disappeared from the US market (hence the big gap in shipments). And FiiO recently announced they’ve formally changed it—perhaps for the second time. The version tested here was purchased in December 2011 but is not the latest one pictured on the FiiO website. The latest version has a gold headphone jack.

MADE IN CHINA PROBLEMS? I’m not sure what’s behind the E10 changes. It might be FiiO switched manufacturing to a different factory to save some money. That’s happening a lot in China lately with Chinese labor rates rising rapidly and build quality fluctuating as cheaper labor is being used for assembly. If you’re curious to know more check out this excellent Wired magazine article on recent problems with Chinese manufacturing (it even features a headphone maker). There are many more articles on this topic. The big players like Apple have locked up the best manufacturing in China and the smaller companies, like FiiO, are often having to really struggle to maintain quality at a decent price.

GAIN SWITCH: The recessed gain switch on the bottom adds about 7 dB of gain in the High Gain position. It also causes the amp to clip with a normal input signal at only around 5 or 6 (50% or 60%) on the volume control. The good news is this switch helps adapt the E10 to various headphones. Use the low gain position with sensitive headphones like IEMs. Only use the high gain position if the E10 won’t get loud enough when set to low. The gain switch has no effect on the line output. Do not use the high gain position for headphones 32 ohms or lower as the E10 will only clip rather than produce more output.

BASS EQ SWITCH: The EQ switch only works on the headphone output not the line output. It causes a broad boost that starts at midrange frequencies and is a constant +5 db below about 100 hz. This requires the E10 to produce over three times as much power below 100 hz and can easily push it into clipping.

INSTALLATION: The E10 installed smoothly without needing any drivers in Windows 7 and XP. Depending on where you’re looking, it’s identified as either “DigiHug USB Audio" or “FiiO USB DAC-E10”. I have no idea what “DigiHug” stands for. A Google search brings up an iPad game and cartoon characters. Perhaps it’s a Chinese thing? The PC’s master volume control, unlike with the E7, remains functional.

USABILITY: The E10 is easy enough to use and, for its size, the ergonomics are reasonable. The gain switch is recessed flush into the bottom of the enclosure so it’s difficult to accidently change the gain. The volume knob is a nice size and there’s not much else to worry about besides the bass EQ switch. Like most FiiO products, they mostly did an impressive job with the industrial design for the price.

HEADPHONE REJECTION: One annoying problem is the headphone jack likes to eject the headphone plug with the slightest tug on the headphone cable. Given that most of us move around while wearing our headphones such tugs can happen relatively often. The jack seems to be poorly designed so the spring loaded contact that’s supposed to lock into the groove on the tip of the 3.5mm plug instead barely hangs on to just the tip. I tried several different headphones and they all reacted similarly. Others have reported similar behavior with their E10s. It’s especially bad for headphones with thicker/stiffer cables. This is the sort of problem someone at FiiO surely was aware of but they shipped zillions of E10s anyway. Not good.

DELAYED REACTIONS: Some have complained the E10 delays producing audio when it’s first fed a digital signal (it defaults to being muted when there’s no digital signal or “digital silence”). I confirmed that’s the case but I didn’t try to measure the delay. This is typically only a minor annoyance except for certain applications like live chat/VOIP where the E10 could clip off essential parts of speech.

SUBJECTIVE SOUND QUALITY: The E10 sounded fine with the headphones I tried. Playing some really wide dynamic range music with my Sennheiser HD650s it seemed to clip on the peaks when I pushed it fairly loud in high gain mode. With my very sensitive Ultimate Ears Super Fi Pro IEMs I could hear some hiss even at low gain but it wasn’t objectionable. I also noticed some channel balance error at low volumes with the Super Fi IEMs. I didn’t much like the bass boost with any of my headphones as it mucked up the lower midrange and vocals. It was also very “boomy”.

LACK OF CONSISTENCY: Older FiiO products (even the $20 E5) have better bass EQ than the E10. It’s disappointing there’s almost no consistency between the bass EQ among FiiO products. Every FiiO product I’ve tested is significantly different and they’re getting worse. This implies either FiiO doesn’t care if they get it right or they really have no idea what’s best. Quality audio products, in my opinion, are designed to a consistent set of goals. Things like headphone bass EQ should be based on what works best with popular headphones and listener preferences. That shouldn’t change from amp to amp or DAC to DAC. It’s always sad to see a company go backwards with their new designs.

MEASUREMENT SUMMARY: With some notable exceptions, the E10 measured about as I expected for an $80 headphone DAC. For those who want to use it to directly drive headphones it’s important to know the limitations of the headphone output. For those who want to use the E10 as only a DAC, and will be using the line output, you can skip the next two paragraphs:

Headphone Output - The E10’s headphone performance was similar to the FiiO E11 and fairly respectable if you can live with a maximum output of 1.5 to 2.5 Vrms depending on the headphones. The distortion performance was acceptable but a bit marginal into lower impedance loads. There’s also some channel balance error in the sample I tested that was audible with my IEMs and measured higher than I like to see. The bass EQ option is far from ideal and more “boom” than bass. Using the EQ may also overload the amp and/or many headphones at loud levels.

Headphone Compatibility - There may be some audible noise with sensitive headphones (especially B.A. IEMs like Shures, Etymotics, Ultimate Ears, etc.). Even the low gain setting forces using only about the first 30% of the volume control’s range with these IEMs. At the other extreme, even set to high gain, the E10 is marginal for having enough output for many popular full size cans like the Sennheiser HD650/600. If you listen at “live” levels to highly dynamic music the E10 can easily clip with such cans. For headphones that require even more output, like the popular 600 ohm Beyers, several AKGs, HiFiMan planars, etc., you’re likely to be disappointed. The good news is the E10 has a low output impedance so it’s well suited for most IEMs and some sensitive low impedance cans like the Denon D2000. When looking at headphone reviews on InnerFidelity, look for a 90 dB SPL voltage of 0.15 Vrms or less (up to 0.25 Vrms might be OK if they’re high impedance and you don’t like loud levels). For headphones rated in dB/V look for a rating of at least 106 dB. For headphones rated in dB/mW things get more complex. See the More Power article.

DAC Performance – The DAC performance of the E10 is a mixed bag. Overall it’s a more respectable DAC than say the NuForce uDAC-2 or any of the inexpensive DACs I recently tested including the UCA202, Creative X-Fi Go, and Asus U3. But its 24 bit performance at 44 Khz was far short of what it should be. The dynamic range from the line out was 97.6 dB which is only 16.2 effective bits of performance. That’s barely better than a good 16 bit DAC. The noise and dynamic range is still likely “good enough” if you use the volume control on the E10 and leave your PC volume turned all the way up. But if you want to control the volume from your PC, you might want to look for a DAC with closer to 18 effective number of bits (ENOB). That allows enough dynamic range to allow penalty free use of the PC’s volume control—the E10 falls short.

E10 vs E7 – The most obvious advantage of the the E10 is significantly more output than the E7 and its ability to drive a wider variety of headphones—especially higher impedance models. The E10 is relatively free of the excessive ultrasonic “crud” that’s always present in the output of the E7 (and E5/6). How much the “crud” is audible is difficult to say but it’s a potential concern with the E7. The E10 DAC can also run in 24 bit mode, and while it barely delivers better than 16 performance, it is still quieter and has more dynamic range than the E7. The E10 generally has lower distortion than the E7. Finally the E7 disables the volume control in the PC’s operating system and the E10 does not.

Here’s how the E10 measures up to some other headphone DAC’s I’ve tested. The ratings use a letter grade from A to F where A is excellent and F is Fail (unacceptable). In some cases the letter grade takes into account more than just the raw number:

*NOTES:The E10 noise is relative to 24 bit performance. The other DACs were tested at 16 bits.

FIRST CLASS:

Small size

Relatively low price

Decent headphone output within its limitations

Low headphone output impedance

Respectable 16 bit DAC performance

Two gain modes

ECONOMY:

24 bit mode only offers 16.2 bits effective resolution

Audible noise with highly sensitive headphones

Channel balance error may be audible

Poor bass EQ is boomy, corrupts midrange, and may cause overload

Line output is nearly 2 dB below 2 Vrms Redbook standard

Headphone plug pops out of the jack easily

Not enough output for some popular full size headphones

Clips above 50% volume in high gain mode

Delay may mute start of audio in some circumstances

Marginally high line output impedance

Potential problems if connected to grounded equipment

Marginally high DC offset—especially in high gain mode

BOTTOM LINE: The E10 has some issues but still is a clear step up from $30 to $40 products like the X-Fi Go and Asus Xonar U3. Overall, if it has enough output for your headphones and you plan to use the volume control on the E10 or a downstream amp, it’s worth considering—especially if you’re on a tight budget. But if you want to control the volume at your PC, you might be better off with a 24 bit DAC that offers more dynamic range and effective bit resolution like the HRT Music Streamer II (which requires a headphone amp like the O2) or a Centrance DACport with the low impedance output option. If you have difficult to drive headphones you may need a dedicated high output headphone amp like the O2 portable amp or upcoming ODA/ODAC.

TECH SECTION

TECH INTRO: I’ve been getting a lot of feedback lately saying things like “nice blog but your reviews are way over my head”. I want to make it clear if you’re not a total audio geek, engineer, scientist, etc. you probably want to stop reading here. All the important stuff has already been summarized above. The rest is mostly just the behind the scenes details for those who care about such things.

TECH INFO: The E10 supposedly uses the setting same AD8397 op amp as the FiiO E11 and AMB Mini3. It’s a high current, and somewhat “high strung” op amp that works better in the E10/E11 than the Mini3. The E10 also supposedly uses the Wolfson WM8740 DAC chip. Unless otherwise noted, I made most measurements using the low gain setting. Several measurements, where applicable, were made from both the line and headphone outputs. I also spot checked some measurements at 24/48 and 24/96 where most performance was similar to 24/44. The E10 is not usable at 24/88 due to a limitation of the USB interface. For more information on my audio measurements, see Music vs Sine Waves, Testing Methods, and Headphone Amp Measurements (InnerFidelity).

VIRTUAL GROUNDS: It would seem the E10, unlike the Mini3 clone E11, does not use a virtual ground. This makes sense because the virtual ground in the E11 prevents using the USB charging port while using it due to the potential severe ground conflicts. The E10, being entirely USB powered, has to operate connected to the PC’s ground. That said, when I connected the E10 to my grounded Agilent scope it freaked out and had massive DC offset. So while there’s no DC voltage between the USB ground and the input or output audio grounds, the E10 seems sensitive to ground loops. Use extreme caution when using it with grounded equipment.

MAXIMUM OUTPUT LEVEL AT CLIPPING: At the low gain setting the E10 will not clip into 35 ohms or higher impedance loads. Below 35 ohms, however, it mildly clips at near full volume with a 0 dBFS signal. At the high gain setting it always clips well before full volume even with no load. The clipping point drops proportionally with the load impedance. This is a bit disappointing as many users will need to be careful not to set the volume too high or they risk severe clipping distortion. But the flip side is having some excess gain for “quiet” recordings. The maximum output above 35 ohms was 1.55 Vrms at the low gain setting and it varied at the high gain setting as the E10 runs out of current below about 35 ohms. It reaches a voltage limit of 2.7 Vrms into no load at hard clipping. This works out to for <1% THD (low gain/high gain):

CLIPPING ODDITIES & CURRENT LIMITS: The E10, when set to High Gain, has the same odd clipping behavior below about 35 ohms as the E11 does. This isn’t surprising as the E10 shares the E11’s output AD8397 op amp and perhaps some power supply details as well. The true clipping point is hard to define but distortion rises dramatically above 1.5 Vrms into 32 ohms. This is very likely caused by the DC-DC converter running out of current and letting the supply rails sag badly. This isn’t ideal behavior as it means the amp is generating substantial distortion over a relatively wide range of output levels into 35 ohms or less before it’s obviously clipping. The O2’s current limiting, by comparison, takes place in the final output stage (versus the E10’s power supply) and the O2 maintains low distortion right up to the true clip point.

LINE LEVEL OUTPUT & GAIN: The term “gain” is a bit hard to define for a device with only a digital input. The Redbook standard for digital audio devices is 0 dBFS of input is supposed to give 2 Vrms of output. With the E10 you only get, at best, 1.65 Vrms. That gives a “gain” of negative 1.7 dB (i.e. the E10 is 1.7 dB below the reference standard). The gain switch has no effect on the line output but adds 7 dB of gain to the headphone output in the High Gain position. The low gain position is still arguably on the high side for balanced armature IEMs and other highly sensitive headphones that only need about 0.3 volts versus the 1.5 volts the E10 delivers. So, with sensitive headphones, you’re stuck using only a small portion of the E10’s volume range which makes the channel balance problems worse and small volume adjustments more difficult.

EXCESS GAIN: For lack of a better description, “excess gain” is my generic term for “extra volume control range” above and beyond the normal clipping point (or desired maximum output) with a 0 dBFS signal. For the E10 in high gain mode it’s about 3 dB into high impedance loads and increases into loads below 35 ohms as the E10 runs out of current and clips sooner. The E10, in high gain mode, starts clipping around “5” or “6” on the volume control (50% to 60% of the range) depending on the load with a typical input signal where the peaks hit 0 dBFS.

0 dBFS DAC PERFORMANCE: The E10 distortion only rose slightly from 0.004% to 0.005% with a 0 dBFS input versus –1 dBFS. This means there’s no significant problem with clipping in the DAC chip or related circuitry (unlike the oddly designed NuForce uDAC-2 which rose to nearly 1% at 0 dBFS).

THD+N vs OUTPUT: The E10 has acceptable but not great distortion performance at 1 Khz. The green line in the graph below represents the upper limit of what’s desirable. In high gain mode the E10 flirts with the limit around 0.75 volts output which is marginal performance. The red line shows the line output which maxes out at 1.65 Vrms with no clipping and reasonably low THD+N. The yellow line shows the odd clipping behavior (likely due to power supply limitations) into 32 ohms mentioned above. The channels were fairly closely matched but not exactly. The aqua and blue lines show the imbalance—likely due to PCB layout problems or compromises. The two blue-ish lines should be on top of each other. At higher output levels into 16 ohms the currents flowing in the PCB traces are highest and that’s where PCB layout is the most critical. See the Legend for a description of each line:

OUTPUT IMPEDANCE: The output impedance is measured at 100 hz as that’s typically where headphone damping is most critical. The E10 dropped from 400 mV no load to 389 mV with a 16 ohm load. This works out to about a 0.5 ohm output impedance which is acceptably low. The line output had a 600 ohm output impedance which is higher than I prefer to see (under 100 ohms is typical). The E10’s line output may have problems with long cable runs, amp inputs with low impedances, passive preamps/volume controls, higher noise, and the input filters in some devices. It will, however, work OK with the O2 and ODA’s input circuitry.

16 BIT RESOLUTION : The following is a 1 Khz undithered sine wave at an extremely low level of –90 dBFS. A proper bit accurate DAC (no upsampling, internal dither, etc.) should reproduce the sine wave as three distinct stepped levels. The E10 performs as expected:

24 BIT RESOLUTION: When the above test is run at 24 bits, if the DAC really supports more than 16 bits, you should get something close to a sine wave. The E10 performs correctly:

FREQUENCY RESPONSE: The frequency response is plotted below from 20 hz to 20 Khz via the line output. It was the same at 16 and 600 ohms from the headphone output. There’s nothing to complain about here and it indicates the E10’s line and headphone outputs are likely direct coupled (no capacitors):

THD+N vs FREQUENCY -1 dBFS: The yellow/orange plot shows the distortion vs frequency via the line output and the blue plot shows the headphone output into 32 ohms at 1.38 volts (-1 dBFS at full volume and low gain). Below about 1000 hz the two outputs are similar. Above 1 Khz the headphone output exhibits rising distortion getting very close to the green threshold line. The drop above 7 Khz is normal due to the intentional bandwidth restriction of the measurement. The line out performance is fine while the headphone output is marginal but acceptable. It should be noted the headphone output is shown at low gain. It was significantly worse at high gain even at the same output voltage:

SMPTE IMD: This is a twin tone test of both low (60 hz) and high (7 Khz) frequencies together in a specific ratio as defined by the SMPTE standard. The dScope ignores the regular THD from each tone and instead looks for distortion created by the two tones interacting with each other. But the raw number doesn’t tell the whole story. It’s also important how much “spread” there is at the base of the 7 Khz tone. Ideally everything should be comfortably under –80 dB and that’s the case with the E10 into 32 ohms at around 1 volt. The line output was a bit better than shown here but similar:

CCIF IMD: This also a twin tone test but at 19 Khz and 20 Khz. This test is far more revealing of audible forms of high frequency distortion than simple THD measurements are above 6 Khz. The reason is the third harmonic of signals 7 Khz and higher are beyond the range of human hearing and beyond the typical cut off frequency of the distortion analysis. But an amplifier with high frequency non-linearities will create even-order distortion products on this test at 1 Khz, 2 Khz, etc. and odd order distortion at at 18 Khz, 17 Khz, etc. All of these are within the audio range and, if above –80 dB, may be audible under some conditions. The E10 struggled a bit (especially in Ch B) with several distortion markers reaching for the green threshold line and one barely exceeding it. it’s notable there are significant differences between the channels. The yellow channel was quite a bit worse likely due to the PCB layout as previously discussed. This is marginal but acceptable performance for 1 volt into 32 ohms. Again, the line output was a bit better:

NOISE & DYNAMIC RANGE 16 BIT: Reproducing a 1 Khz signal at a very quiet –60 dBFS the noise is measured by the dScope removing the 1 Khz signal and its harmonic distortion and calculating the left over noise out to 22 Khz. This test is referenced to the maximum clean output of the device at 0 dBFS. A perfect 16 bit DAC has 96 dB of un-weighted dynamic range. Most audio noise measurements supplied my manufactures are A-Weighted which adjusts for the sensitivity of human hearing to noise. Using the line output, and referencing its maximum output of 1.65 volts, the dynamic range (DNR) is approaching the best you can get from 16 bits which is 96 dB. This shows the DAC, not the analog circuitry after it, is the limiting factor and about as good of performance as you can expect from a 16 bit DAC. The headphone output had only slightly more noise so the DAC chip itself seems to be the dominant noise source in the E10:

NOISE & DYNAMIC RANGE 24 BIT: Switching to 24 bit mode, with everything else the same as above, things don’t improve nearly as much as I would have expected. If you look closely you can see the central part of the noise floor drops about 10 dB. That’s what I would expect. But, unfortunately, there are a bunch of new noise components apparently related to operating the DAC chip in 24/44 mode and reproducing the –60 dBFS 1 Khz signal. The result is the total A-Weighted dynamic range is 97.6 dB. That’s only about 2 dB better than the 16 bit result above and only 16.2 effective bits of performance. While this is still OK for applications that use the E10’s volume control it might be a problem for those wanting to leave the E10 volume turned up and use only the PC’s volume control. Especially with sensitive headphones you may hear some noise from the E10 under similar conditions. I’m not sure what’s causing the extra noise but my guess would be the digital filtering on the Wolfson DAC isn’t optimized for 24/44 operation:

DAC LINEARITY & 24 BIT ABSOLUTE NOISE: Linearity measures how accurately a DAC can reproduce very low levels. A DAC should be within +/- 1 db at –90 dBFS and many remain linear to even lower levels. The E10 does fine in the linearity department, but one channel has much more high frequency noise than the other in 24/44 mode. The extra noise goes away in 16 bit mode. This seems related to the same problem discussed above but here it’s low enough in level to not be a big problem. The absolute noise is 49 uV or –98 dBu which is quiet enough for most full size cans, but not for total silence with really sensitive IEMs—especially if you control the volume at the PC:

MODULATION NOISE: Ideally the noise floor of a DAC will remain constant regardless of the signal level. In practice, this is rarely true and the noise typically rises with the signal. If the noise is high enough this can be an audible problem as the noise will fluctuate in response to the music—something the ear seems especially sensitive to. The important criteria is how flat the noise curve is with respect to the level and how far below the green threshold it is. The blue-sih lines are the two channels in 24/44 mode while the orange/yellow lines are the two channels at 16/44. At lower levels the E10 is quieter in 24 bit mode but, interestingly, at around –12 dBFS and above, it’s quieter in 16 bit mode. Again, I suspect this is related to the problem in the previous two tests in 24 bit mode. Everything is below the green line, and hence likely inaudible, but this is more odd behavior. The blue line should be at least 6 below the orange line across the entire graph:

CROSSTALK: Into 32 ohms the E10 measured a consistent 55 dB of crosstalk across the audio range. The flat result implies it’s almost entirely limited by the impedance of the ground circuitry and shared common ground in the headphone jack. It’s an acceptable result but just below the green threshold at –50 dB. Using the line output the crosstalk is about –95 dB best case at low frequencies and steadily rises to about –55 dB at 20 Khz. This shows high frequency coupling in the PCB layout and volume pot. This is also an acceptable result:

CHANNEL BALANCE: With the volume set at 40% (a typical setting) there was about 0.25 dB of channel balance error as can be seen below. I didn’t do my usual graphing at many volume settings, but adjusting the volume knob and watching the dScope’s live reading of channel balance, the error was somewhat worse than usual overall. At my usual level of –45 dB below full volume it measured 1.3 dB which is over the 1 dB threshold and generally audible. At even lower levels the error was as high as 5 dB while at higher levels it varied randomly with the volume setting but was generally around 0.25 – 1.0 dB. This is marginal performance and a sign FiiO probably didn’t spend enough money on a decent volume pot:

JITTER & INTERCHANNEL PHASE: Here’s the spectrum from the dScope’s J-Test for jitter. It’s a special signal at 1/4 the sampling rate with the lowest bit toggled on and off. It’s not possible to summarize this test in one number. What matters most are the number and height of symmetrical distortion components mirrored on either side of the 11025 hz signal which indicate high frequency jitter components. And the amount of “spread” at the base of the signal indicates the relative amount of low frequency jitter. Ideally nothing should reach above –110 dB (with a slight allowance for exceptions near the main signal). But, it’s worth noting, there is considerable debate about the audibility of various amounts of jitter (see: Jitter Does it Matter?). The E10 stays under the green guideline but barely. The result is shown for both 16 and 24 bit modes. Besides the noise floor dropping in 24 bit mode not much else changes. The phase error, as would be expected with a decent DAC chip like the Wolfson, is essentially zero. This is an acceptable, but not great, performance:

BASS EQ: I’m not very impressed with the E10’s bass EQ. It reaches well up into the midrange which makes vocals (especially male vocals) sound oddly “tubby” and thick. It has almost full boost at 100 hz which is more “boom” than true bass. And, finally, it doesn’t taper off at really low and subsonic frequencies. This means when playing content with a lot of really deep bass energy (like some dance music) the E10 may clip and/or overload your headphones (bottom out the drivers) when using the EQ. I prefer EQ curves that peak around 50 hz and rapidly taper off on both sides. The E10’s EQ is far from that ideal and notably worse than the EQ in some earlier FiiO headphone products. Going backwards is not progress:

CLIPPING PERFORMANCE: The E10’s headphone output clipped cleanly at around +/- 4 volts peak in high gain mode into 600 ohms. Dropping the load to 16 ohms causes the E10 to be current limited and it clips at just over 2 volts peak. In both cases the clipping was clean and close to symmetrical even when viewed on a high speed scope. There was only a small amount of ultrasonic “crud” from the DC-DC converter in the E10 (not visible here). The E10 is massively better in this regard than the TI chip amp based E5, E6 and E7:

IMPULSE RESPONSE: The E10 preserves absolute polarity and uses a classic linear phase digital filter with pre and post ringing. The same headphones and capacitive test load that gave the MacBook Air fits is handled by the E10 with minimal fuss. Unless you’re a fan of minimum phase filters (no pre-ringing), there’s nothing remarkable here:

DC OFFSET: The E10 had significantly higher DC offset than I’m used to seeing, In the low gain mode it was 14 mV in both channels. In the high gain mode it was 30 and 31 mV. This is marginal for highly sensitive IEMs and also causes some noise when you plug the headphones in. As mentioned earlier it’s apparently a DC coupled design and that may have been a poor choice without otherwise managing the resulting excessive DC offset. FiiO is clearly not sweating the hidden details like they do with the visible ones (like the case, controls, packaging, etc.). It’s form over function.

TECH COMMENTS: With a couple of notable exceptions, the E10 measured about like I expected it to. The exceptions are:

24 Bit Performance - The biggest disappointment, by far, was the 24 bit performance using an industry standard –60 dBFS 24/44 signal. Wolfson quotes 117 dB A-weighted SNR at 24/48 (19.5 ENOB) for the DAC chip and the E10 only delivers about 97 dB (16.2 ENOB). I don’t expect any DAC to meet the chip’s datasheet spec, but the E10 missed by a huge 20 dB margin which rates a solid FAIL from an engineering perspective. While the E10 performs better at 48 Khz that’s only useful for watching DVDs unless you want to resample 99% of the digital music out there. Re-sampling likely creates more problems than operating the E10 at 48 Khz solves. The 24/44 issue showed up in several tests so it’s clearly not some measurement fluke. It indicates a potential implementation problem—likely in how FiiO is configuring (or failing to properly configure) the Wolfson chip for 24/44 operation. When there’s no microcontroller the options are often very limited with communication between the USB interface and the DAC chip. The result is the DAC chip may fall on its face for certain data formats. That seems to be the case with the E10 and 24/44.

Poor Choice of DAC Chip: If the above is an unavoidable problem without adding a microcontroller it’s my opinion FiiO chose the wrong DAC chip. Lots of small “boutique” audio manufactures seem to put FOTM chip brands and part numbers ahead of common sense. They use parts popular among audiophiles but they’re often completely the wrong part for that particular design. That may well be the case for the E10 and for the E11 which uses the same OPA690 op amp as the Mini 3. The OPA690 is not even remotely designed or specified for audio use and holds back the performance of both the E11 and the Mini3. The WM8740 may have been a similarly poor choice for the E10. I just don’t get the logic behind such design decisions when it so obviously compromises the performance.

Odd Clipping/Current Limiting – Like the E11, the E10 struggles with loads below about 35 ohms. I’m guessing the DC-DC converter runs out of beans and the supply rails sag badly. That likely creates the very odd distortion behavior above 1.5 Vrms into 32 ohms or lower. The E10 would be a poor choice for low impedance current hungry headphones like most planars. This creates a situation where the amp starts distorting relatively severely before it’s obviously clipping.

Limited Voltage Output – The line output fails to meet the Redbook standard of 2 Vrms and the headphone output, in high gain mode, maxes out at only about 2.6 Vrms which is well short of the 5+ Vrms many headphones require including the popular Beyer DT880-600. It’s also a marginal output level for even many of the popular full size Sennheisers and AKGs. But it’s only fair to consider it’s an $80 tiny USB powered headphone DAC. Some compromises are to be expected. At least it outperforms all the cheaper USB headphone DACs I know of.

Channel Balance Error – The channel balance was a bit disappointing and notably worse than devices I’ve tested that use an Alps RK09 volume pot such as the O2 amp. FiiO probably chose a cheaper pot to keep the price down. The parts and labor costs of the E10 likely total less than $20 in the volumes FiiO buys at. Again, you have to expect compromises at the E10’s price.

Marginal THD+N & CCIF IMD – The noise floor was higher than I would like to see in 24 bit mode and the distortion driving 32 ohm headphones was a bit excessive under some conditions as well (CCIF IMD and above THD 3 khz). This indicates the AD8397 implementation and/or PC board layout are less than ideal. There was also some significant channel asymmetry between the high frequency distortion and noise performance indicating a compromised or flawed PCB layout. Again, given the small size and low price, this isn’t too surprising.

Marginal DC Offset – The DC offset is significantly higher than I like to see. It’s many times the typical offset of the O2. FiiO probably should have addressed this either using DC blocking caps or a DC offset compensated design. It’s something few users will be aware of but indicates they cut some serious corners in the design and/or consider marginal specs acceptable.

FINAL WORDS: If you’re OK with its limitations, and for the right applications, the E10 is worth its $80 price and a better choice than some of its competitors. I would choose the E10 over the NuForce uDAC-2, for example, without hesitation. Those with more challenging headphones may want to consider adding a higher quality headphone amp like the O2. And those who prefer to control the volume from their PC may want to choose a 24 bit USB DAC with higher dynamic range like the Centrance DACport with the low impedance output option. When used within its limitations, the E10 is decent headphone DAC for $80. But it’s compromised in several areas likely due to the low price, small size, and being USB powered.